<div class="box">
  <div class="row">

<div class="flex-container">
  <div class="item"></div>
  <div class="item"></div>  
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
</div>
        
  </div>
</div>


  

*, *::after {
  box-sizing: border-box;
}

.box {
  display: block;
  top: 100%;
  width: 100%;
  right: 0;
  left: 0;
  background: #fff;
  z-index: 9;
  border: 1px #000 solid;
}
.row {
  max-width: 1200px;
  margin: 0 auto;
  overflow: hidden;
}
.flex-container {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  align-items: normal;
  margin: -30px 0 0 -30px;
  position: relative;
  z-index: 0;
}

.flex-container::after {
  content: '';
  position: absolute;
  right: 0;
  top: 0;
  width: 170px;
  height: 100%;
  background-color: #fff;
  z-index: -1;
}

.item {
  width: 170px;
  position: relative;
  margin: 30px 0 0 30px;
  min-height: 200px;
  background: #f1f1f1;
}

.item:not(:last-child)::after {
  content: "";
  position: absolute;
  width: 30px;
  height: 30px;
  left: 100%;
  bottom: 100%;
  border-radius: 50%;
  border: 1px #000 solid;
  z-index: -2;
}